Increased demand for sulphur-containing fertilizers steins from the discovery that low crop yields in certain cases may be related to deficiencies in sulphur in the soil. An example of a species with high sulphur requirements is Canola. Canola is an important cash crop in Alberta, Canada, and has high sulphur requirements at any growth stage. A shortage of sulphur can cause serious reductions in crop yield and quality.
Manufacturing processes for sulphur-containing fertilizers of the phosphate type often involve the use or incorporation of sulphates. A disadvantage of sulphates is that they are very mobile in the soil and easily leach out of the root zone, effectively making the sulphate nutrient unavailable to the plants. Elemental sulphur is not leached out of the soil as readily as sulphates. Instead, micron-sized elemental sulphur particles (e.g. with size from 1 to 200 μm) are oxidized to sulphate sulphur, which is the form utilized by the plants, by soil bacteria during the cropping season. Elemental sulphur can therefore be considered a slow (timed) release form of plant nutrient sulphur that is less prone to leaching out of the crops root zone. It is, therefore, advantageous to have a large proportion of the sulphur in fertilizers present as elemental sulphur. Furthermore, elemental sulphur offers some additional benefits in agriculture, including acting as a fungicide against certain micro organisms, acting as a pesticide against certain soil and plant pests, assisting the decomposition of plant residues and improving phosphorus and nitrogen nutrient utilization and reducing the pH of alkaline and calcareous soils.
Thus, it is advantageous to incorporate sulphur in sulphur-containing fertilizers as elemental sulphur.
Processes for the manufacture of sulphur-containing fertilizers, wherein elemental sulphur is used, are known in the art.
NZ 213682 discloses a method for providing sulphur for use in a sulphur-containing fertilizer wherein liquid sulphur is added to phosphoric acid, wherein the phosphoric acid is in a high energy state of shear in a high energy vortex.
U.S. Pat. No. 4,372,872 discloses a process wherein a suspension of sulphur is produced by agitating an aqueous medium with a high shear mixer, and introducing sulphur (in particulate or molten form} into the agitated medium. The sulphur suspensions can be applied to the soil. The dispersions obtained by this process have the disadvantage that the particle size and particle size distribution of the elemental sulphur-containing fertilizer obtained leave considerable room for improvement as sulphur will separate from the continuous phase if left without intense agitation.
WO 2010/102389 discloses a process for converting lump sulphur into a micron sized powder whereby the sulphur is micronized in the molten form in a superheated dispersant solution. Said process is a continuous process.
The use of superheated dispersant solution involves preparing the dispersant solution and effecting the micronisation under pressure, thus expending high amounts of energy in doing such.
US 2010 288005 discloses a method for producing tablets made of a mixture of a plurality of materials, and a method for producing a sulfurous fertilizer whereby the tablets are formed using a drop former whereby the sulphurous fertilizer is micronized by application of ultrasonic sound immediately upstream of, or within the drop former.
U.S. Pat. No. 4,330,319 discloses a process for the manufacture of urea sulphur fertilizer whereby the sulphur has a particle size of smaller than about 100 micron and whereby molten sulphur and molten urea are passed through a mixing device through which a pressure drop of at least 200 kPA is applied.
U.S. Pat. No. 7,998,235 discloses a method for the production of a urea fertilizer with elemental sulphur from sulphur in liquid stage and a liquid urea melt. The method uses an additive that is temperature stable and amphoteric.
Object of the present invention is to provide a low energy method for preparing a stable emulsion of micro-encapsulated molten elemental sulphur in a liquid, that also display an improved particle size and particle size distribution.
In addition, the present invention provides a process for preparing an elemental sulphur-containing fertilizer, wherein the particle size of the elemental sulphur particles can be easily controlled.